Artificial bone or tooth prosthesis material

ABSTRACT

A prosthesis material useful for artificial bones or teeth is provided in the form of a heat-consolidated body composed essentially of a dense structurally integrated mixture of discrete microcrystals of a calcium phosphate compound together with discrete microcrystals of a refractory compound, such as the mineral spinel, aluminum phosphate, or aluminum oxide. The preferred calcium phosphate compound is whitlockite, but it can be used in combination with other more soluble calcium phosphate compounds.

D United States Patent 1 1 1 1 3,787,900

McGee Jan. 29, 1974 1 ARTIFICIAL BONE R TOOTH 2,479,504 8/1949 Moore eta1. l06/38.3 PROSTHESIS MATERIAL 3,662,405 /1972 Bortz et a1. 106/40 R X3,443,261 5/1969 Battista et al. 128/92 C X Inventor: Thomas McGee,Ames, Iowa 3,510,322 5/1970 Higashi et a1. 106/35 [73] Assignee: IowaState University Research OTHER PUBLICATIONS Foundation, Ames, IowaAmerican Ceramic Society Bulletin, Volume 49, Flledi J 9, 1971 Jan-June1970, at page 482. [21] Appl. No.: 151,580

. Primary ExaminerA1lan Lieberman [52] US. Cl 3/1, 32/8, 32/10 A,

32/12, 32/15, 106/35, 128/92 c, 128/92 G ABSTRACT [51] f Ame 13/08 (299k3/00 A prosthesis material useful for artificial bones or [58] new 9Search 32/8 10 10665: teeth is provided in the form of aheat-consolidated 106/38'27 39 40 body composed essentially of a densestructurally inte- 128/92 92 grated mixture of discrete microcrystals ofa calcium phosphate compound together with discrete micro- [56]References C'ted crystals of a refractory compound, such as the mineralUNITED STATES PATENTS spinel, aluminum phosphate, or aluminum oxide. The2,072,212 3/ 1937 Moosdorf et a1, 106/38.9 preferred calcium phosphatecompound is whitlockite, 2,522,548 9/1950 Streicher 106/38.9 X but itcan be usedv in combination with other more sol- 2,486,131 1 1 1/1949Weyl I 106/46 uble alcium phosphate compounds. 3,473,599 10/1969 RoselO6/38.3 X 2,726,963 12/1955 Jackson 106/46 11 Claims, N0 DrawingsBACKGROUND Bone prosthesis are often needed for temporary or permanentuse in men and animals. These may be to provide support until a fractureheals, to replace bone lost by accident or disease, to strengthen bonewhich has atrophied or lost mineral content, to elongate a bone which istoo short or for a variety of other purposes.

Most individuals lose one or more permanent teeth during their lifetime.A need to permanently replace individual teeth exists. Sometimes thealveolar ridge becomes too thin to support conventional false teeth.Building this ridge with or without artificial teeth is needed for thosesuffering from this defect.

Most prior art bone prostheses are metals. Some of these are Vitalluim,stainless steel, chromium and titanium. These are used as spikes andsplints and to replace ball and socket joints. They do not bond to thebone and are removed after normal healing whenever possible. The highelectrical and thermal conductivity and the foreign chemical natureoften results in undesirable side effects and unsatisfactoryperformance. Although mandibles have been partially replaced by astainless steel truss the problem of joining to the remaining bone andthe support of teeth and chewing forces has usually been insurmountable.Organic resins or silicone rubbers have sometimes been used to build upbones but these have insufficient strength, do not bond to the bone, areoften rejected and are sometimes carcinogenic. This applicationdiscloses ceramic compositions which are compatible with natural boneand which do not have the deficiencies of metals or plastics.

DISCLOSURES OF. INVENTION In preparing a prosthesis material inaccordance with the present invention, a principal ingredient is one ormore calcium phosphate compounds. Such compounds can be utilized in theform of fine crystalline powders, either being obtained in this form, orground to an average particle size of minus 200 mesh (American StandardScreen). Any of the various calcium phosphate compounds can be used inthis form, but it is preferred to include at least a major portion ofthe calcium phosphate mineral known as whitlockite, which has theformula Ca (PO This compound is the least soluble in water, saliva, ortissue fluids of the known anhydrous calcium phosphate compounds. Theothers are also included in the calcium phosphate compounds of CaOzP Oratio of 1:1 to 4:1. Known crystalline compounds within this ratioinclude Cap- Ca P O Ca P O and Ca P O All the calcium phosphatecompounds within this ratio can be produced from other raw materials,such as CaCO and P O and are included within the broad scope of thisinvention.

Minor ingredients can be added to calcium phosphate compounds to causedifferent crystal structures with similar solubility characteristics.For example a small amount of fluorine or chlorine can be added toproduce an intermediate compound Ca PO F or Ca (PO Cl respectively andsuch additions are included in the scope of this invention where theCa:P ratio is within the range 1:4 and the composition is essentiallyanhydrous. Similarly replacement of part of the Ca with Mg, Sr or Zn orsimilar divalent ions is an obvious modification which is included.

The other essential ingredient of the prosthesis material is arefractory compound which does not react with or form mutual solidsolutions with calcium phosphate compounds. Although such'refractorycompound performs an important function in the prosthesis material,

it desirably is substantially inert, that is, non-reactive, with respectto the calcium phosphate compound, making it possible to prepareheat-consolidated mixtures containing discrete microcrystals of thecalcium phosphate compounds in eminent association with discretemicrocrystals of the refractory compound.

The mineral spinel, which has the formula MgAl O is a particularlydesirable refractory compound. Other refractory compounds which can beused include aluminum phosphate (MPO,) and alumina (A1 0 Additionally,mineral oxides having the spinel-type crystal structure can be useful,providing they otherwise meet the requirements set out above. Suchcompounds will have the general structure A8 0 where both A and B aremetal ions, usually different metal ions. For example, the ion A can bemagnesium, strontium, barium, or zinc. The ion A can also be divalentforms of the transition elements, such as iron, cobalt, and nickel. Themetal ion B can be aluminum, or a trivalent form of the transitionelements such as iron, cobalt, or nickel. Further, although A and B arepreferably different metal ions, this requirement is satisfied where Aand B are the same metal, but are in different valence forms.

In general, the prosthesis material will contain a substantialproportion of both the phosphate compounds and the refractory compounds.For example, the prosthesis material after heat-consolidation, maycontain a total of from 15 to percent by weight of the calcium phosphatecompounds, and from 25 to percent by weight of the refractory compounds.

To provide for relatively limited solubility of the calcium phosphatecomponent, it is desirable to use at least 45 weight percent ofwhitlockite of the total calcium phosphate. In other words, from 0 to 55weight percent can be the more soluble calcium phosphate compoundslisted above. While whitlockite can form the only calcium phosphatecompound, it may be desirable to control the relative solubility, and toprovide for some short term surface solubility by incorporatingcontrolled proportions of the other calcium phosphate compounds incombination with whitlockite. For example, from 45 to 99 weight percentof whitlockite can be used together with l to 55 weight percent of atleast one other phosphate compound from the group of compounds havingCaO:P O ratios within 1:1 and 4: 1. Preferred compounds are CaP O Ca P Oor Ca P- 0 Control of the relative proportions of the calcium phosphatecompounds can also be based on the ratio of calcium to phosphorous. Ingeneral, it is desirable to employ a ratio of from 0.3 to 2.0 moles ofcalcium per mole of phosphorous. In certain preferred embodiments, aratio of calcium to phosphorous of 0.5 to L2 moles calcium per mole ofphosphorous can be used.

In preparing the mixtures of the ingredients for heat consolidation, itwill be desirable to also have the refractory compound in a fine stateof subdivision, such as an average particle size of less than 200 mesh(American Standard Screen). Where the refractory compound is formed insitu, it is also desirable to have the constituents react to form therefractory compound in a similar fine state of subdivision. Therefractory compound will also be in crystalline form if used as such, orwill be formed and crystallized during the heatconsolidation. Theingredients should be thoroughly and uniformly mixed. For example, allingredients can be ground together in a ball mill, thereby assuring bothuniform mixing and a fine state of subdivision.

The prosthesis material is formed from the mixture of ingredients bywell known techniques of ceramic engineering, namely, vitrification,sintering, or casting. Casting is melting in a crucible and pouring intoa mold where crystallization occurs. Vitrification is heat consolidationin the presence of a liquid phase while sintering is heat consolidationwithout the presence of a liquid phase. In general, the temperaturesrequired for sintering or vitrification are those which produce amaximum bulk density together with a minimum apparent porosity. Even forthe sintering technique, the temperatures required will be well belowthe melting temperatures of the refractory material. To promote the heatconsolidation, especially when vitrification is the technique employed,minor amounts of fluxes, or liquid-phase providing components, can beutilized. In the ceramic arts, such ingredients are usually referred toas mineralizers. In terms of the total weight of the mixture beingfired, they will usually constitute less than 5 percent by weight, and,of course, can be omitted entirely where the consolidation is bysintering without the presence of the liquid phase. Among themineralizers which can be used are boric oxide, which can beadded in theform of boric acid, cryolite (Na AlF and titanium oxide TiO Othermineralizers include the fluorides, nitrates, and sulfates of the alkaliand alkaline earth metals. Such ingredients do not change the essentialproperties of the prosthesis material, but only promote the desired heatconsolidation to provide a dense structurally integrated product. Afterheat consolidation, whatever the technique employed, the resultingmaterial will be characterized bydiscrete microcrystals of the calciumphosphate compounds in intimate association with discrete microcrystalsof the refractory compounds. In general, the average size of thecrystals will be less than microns diameter.

Prior to firing, the mixture of ingredients can be placed in a mold toprovide the desired final shape, or melted and poured into a mold toprovide the desired shape, or the material can be formed in largerbodies, which can then be cut to the desired size and shape for use asbone or tooth implants.'During firing, the mixture will shrink andconsolidate, and become impervious with minimized porosity, and greatlyincreased structural strength. The optimum temperature for the heatconsolidation can be readily determined by standard ceramic engineeringprocedures, a series of samples being run to determine at whattemperature the apparent porosity reaches a low or minimum value inassociation with a high or maximum value for the bulk density. Apparentporosity and bulk density may be determined by the basic proceduresdescribed in: Standard Method of Test for Water Absorption, ApparentPorosity, Bulk Density and Apparent Specific Gravity of Fired PorousWhiteware Products, ASTM Designation C 373-56, Pages 326-328, 1970Annual Book of 4 ASTM Standards, Part 13, American Society for Testingand Materials, 1916 Race St., Philadelphia, Pa.

Further details for practicing the present invention are shown in thefollowing examples, but it should be understood that the invention isnot limited to the specific examples.

EXAMPLE 1 Equal molar ratios of Ca (PO.,) whitlockite, and MgAl O spinel(from MgCo and A1 0 of TiO H and Na AlF as mineralizers using thefollowing raw materials to produce approximately a 500 gram batch:

These materials were ball milled with water for 14 hours. The slurry wasdried and the cake was broken with a mortar and pestle. The powder wasmoistened with 5 percent polyvinyl alcohol solution and pressed with10,000 psi pressure in a steel moldto produce 11 inch diameter discs.These were isostatically pressed at 20,000 psi and fired for 8 to 12hours to a thermal gradient furnace. Heat consolidation was achieved byvitrification due to the presence of the mineralizers. Although thetemperatures employed were well below the melting temperature of spinel,the magnesium carbonate reacted with the aluminum oxide to producecrystalline MgAl O in situ with the evolution of carbon dioxide. Oneadvantage of the in situ formation is that the raw materials are morereadily available and less expensive than the mineral spine].

The results of these tests are shown in the following table:

Based upon these results, additional specimens were produced and firedat l,l45C as an optimum consolidation temperature. X-ray diffractionanalysis revealed whitlockite, Ca (PO and spinel, MgAl O as the majorconstituents.

Some of these specimens were ground to pass a 40 mesh testing sieve.After washing in acetone 10 grams of the powder was boiled for 14 hoursin 50 ml distilled water. This was filtered, dried and weighed. Weightloss was less than 0.001 gms. The filtrate was titrated with 0.02 N H 80using methyl red as an indicator. By assuming simple calcium ionsolution this titration indicated 0.014 percent solubility- Others ofthe specimen discs were polished by standard techniques to producespecimens for optical microscopic examination. These polished to a highgloss with a natural dental enamel appearance. Pores were round andisolated. The microstructure was one to five 6 micron discrete grains ofthe two intermixed phases, Firing ppa B the spinel and Whitlockite.Electron microprobe analy- Temperature pomsuy Denmygmlcc sis of thedistribution of the elements Mg, Al, Ca and 1350"C 1.95 3.01 P revealedthat the Ca and P were associated and sepa- 3-28 33? rated from the Mgand A1 which were also associated. 5 205C 14:30 This demonstrated thatthe spinel had not appreciably reacted with the calcium phosphate.

Additional ones of the specimens were implanted X-ray diffraction of thespecimens fired'at 1,350C subcutaneously i d Th h l i did not brevealedwhitlockite and spinel to be the only phases Serve any h f l reactions.present. When tested for solubility as described in Example I less than0.001 grams from 10 grams was lost.

When the filtrate was titrated no significant calcium Example h wasfound in solution. When implanted subcutaneously in a dog there was noharmful reaction.

In a further experiment, following the procedure of 15 Using the SameProcedure, teeth can be P p for Example 1 Specimens 15 mm long and 4 mmi implanting. If desired, the base of the teeth can be ameter wereprepared. Forty percent naphthalene crysground and tapered to Provide adOVe'tah, using a Stantals were incorporated in one half when the powderwas dard grinding machine and an aluminum Oxide Stonepressed to produce200 to 500 micron pores in that end f y a h P l can h used- In either ftthe Specimens were fi d These were implanted case, the aw bone inWhlCl'l the tooth s to be implanted in a dog in the bony Sockets where acanine and a molar. will be cut to provide a correspondlng recess. Wheretooth had been extracted. The porous end was placed desired for the baseof the heath to have p y this deepest in the socket and the dense endwas covered can h accomplished by addlhg a Volatile materlal w t with ftissue f the gum Aft 8 weeks to firing, such as the naphthalene crystalsreferred to 1n vealed normal bony structure about the tooth. The ra-Example diologist interpreted the X-ray examination as showing normalperidontal tissue at the margins. After 10 weeks E m le IV the gum wasincised and extraction attempted. The tooth had bolnded 9 the so wellthat the Elsual x A prosthesis material containing 1 mole Ca (PO totraction was1mposs1ble.Th1s was not ust soft tlssuebut 3 moles ofMgAl2O4 was made using Mgcos, A1203, a very strong bond Wl'llCh 1sbelieved to be mmerallzed CaHPOq and Caw(OH)2(PO4)6 as raw materialsusing bone. At no time were undes1rable mflamatory or rethe f ll iformula; jection reactions observed. The animal remained healthy.

Example 111 MgCO 56.28 gm A1 0 68.06 W CaHPO, 10.07

Equal molar ratios of Ca (PO and MgAl O (by in 4Q calhomhpohfi 353 msitu reaction) were incorporated in a body, with the adg dition of 5%TiO and 1% Na AlF by weight as mineralizers. A 500 gram batch was madewith the following 1 raw molecules in weight percent: The chemicals weremixed as dry powders with a mortar and pestle. They are moistened with 5percent polyvinyl alcohol solution and pressed as 25 mm discs Ingredientweighugms) with a steel mold at 2,000 lb/in applied load. These M co92.7 were then placed in rubber envelopes and isostatically 2 3 111.9pressed (placed in an hydraulic cylinder filled with 52 32 water andsubjected to hydraulic pressure of 15,000 no, 2 ,3 lb/in The discs wereplaced in a furnace and fired to sinter them. The properties afterfiring for one hour at 548's the indicated temperatures are shown below.

Firing Linear Apparent Bulk Temperature Shrinkage, Porosity, Densitygm/cc 1 C 2.87 56.] 1.46 1250C 3.20 55.0 1.47 1425C 10.3 46.3. 1.831500C 14.9 8.7 2.74

This composition was prepared as disc specimens in the same manner asExample I. When tired in a gradient furnace the following propertieswere obtained:

As shown, without the mineralizers this composition must be fired tohigher temperatures to cause heat consolidation (sintering). Theresidual porosity after firing 7 8 to l,500C is still appreciable.Higher firing would re They were weighed, mixed with a mortar andpestle, duce it further. The product at l,5 C would be suitmelted in arefractory crucible at 1,450C and poured able for applications whereimpermeability is not esseninto a preheated porcelain crucible. Theresult was a t ial. strong dense white crystalline product which had anap- A disc of the -l,500C. sintered 1:3 molar ratio of parent porosityof 0.0 percent and a bulk density of whitlockite to spinel was implantedsubcutaneously in 2.86 grams/cc. a dog. After 5 weeks the implant wasremoved and the Prosthesis materials prepared in accordance with theassociated tissue subjected to histological analysis. The presentinvention are expected to have many advanpathologist reported noundesirable reactions. He reported a thick connective tissue capsulewith entrapped" 1Q atrophic muscle. The lining of the capsule wasimmature fibrous tissue with a few foci of fibrin attached.

tages. They should be suitable for bone replacements, including suchprostheses as permanent bone bridges, bone segments, and artificalteeth. In these applications, the prostheses material will be compatiblewith vExam l V bone and surrounding tissues and blood. Furthermore,

p e v the prosthesis material wlllhave adequate strength to permitnormal body stresses, and will provide low thermal and electricalconductivity. The prosthesis materials are non-toxic, and provide amechanism for bonding to the natural bone, the implanted prosthesisundergoin mineralization to inte rate it' to the bone. Where 2 -1)2' 2 QEI O Ca3(PO")2 4A1PO4 de sired, the prosthesis maferial can be ground orpol- 2 ished to provide smooth hard surfaces for joint replacement, orfor the upper portions of teeth. Forartificial teeth applications, theprosthesis material will resist bacterial and food corrosion, and-willprevent conduction of heat from the oral cavity to the gums and jaw.Further, the prosthesis material is adapted for use as complete teeth,or as the base of teeth for receiving caps, will promote normal gum andperidontal membrane structure.

I claim: 1. A strong dense artificial bone or tooth prosthesis materialin the form of a crystalline ceramic body which has beenheat-consolidated to a substantially A prosthesis material ofwhitlockite, Ca (PO.,) and 15 berlinite, AlPO.,, was made using Ca (H PO'H O and A1 0 as the starting materials according to the followingreaction:

The raw materials, 78.9 grams of Ca(H PO 'H O and 21.1 grams of A1 0were mixed as powders and pressed into discs as described previously.These were fired at 1,330C to obtain a bulk density of 2.15 gm/cc and aporosity of 13.6 percent. Boiling a powdered specimen for 6 hours indistilled water produced no appreciable weight loss verifying theinsoluble nature of the prosthetic. This composition does not begin tosinter until heated above 1,300 and melts at about 1,380C. It has anarrow firing range but excellent solubility properties.

mp I maximum bulk density with minimized apparent porosity, said bodyconsisting essentially of a mixture of dis- A prosthetic material wasmade with a 1:1 ratio of crete microcrystals ofa calcium phosphatecomponent Ca ,(PO.,) to A1 0 from the following formula. having a CaozPO ratio of 1:1 to 4:1 together with discrete microcrystals of arefractory component selected from the group consisting of MgAl O MPO,,A1 0 CMHQPOM H2O 159 Weight and mlxtures thereof, sa1d body containingfrom 15 to 10( )2l 4)a 39.4 75 percent by weight of said calciumphosphate com- 7 A110: ponent and from 25 to 85 percent by weight ofsaid re- 1000 fractory component.

2. The prosthesis material of claim 1 in which said 45 calcium phosphatecomponent is whitlockite. Specimens were prepared by the methods ofExam- 3. The prosthesis material of claim 1 in which said reple I andfired to produce the following properties: fractory compound means isMgAl O Firing Linear Apparent Bulk Temperature Shrinkage, Porosity,Density gm/cc 1140c 0.1 37.1 2.04 l300C 0.2 24.4 2.54 [380C 23.2 0.02.43

Firing to 1,38l)C. produced a dense nonporous ma- 4. A strong denseartificial bone or tooth prosthesis terial which did not loseappreciable weight when material in the form of a crystalline ceramicbody crushed and boiled for 6 hours. which has been heat-consolidated toa substantially maximum bulk density with minimized apparent poros--Example VII ity, said body consisting essentially of a mixture of dis- Aprosthetic material composed of a 1:1 olar atio crete microcrystals of acalcium phosphate component 0f a( 4)z and AIPQ: was made y melting andCastselected from the group consisting of Ca (PO ,CaP- ing. Thiscomposition is 39% CaO, 11.7% A1 0 and 0 Ca P O Ca P O and mixturesthereof, together 49.3% P 0 by weight. The raw materials were: withdiscrete microcrystals of refractory component selected from MgAl O AlPOA1 0 and mixtures thereof, said body containing from 15 to percent by64.7 weight camzponzflzo weight of said calcium phosphate component andfrom 15.2 weight A1 0, 25 to percent by weight of said refractory compo-20.1 weight Ca,., 01-1),(P0.),, nent' 5. The prosthesis material ofclaim 4 in which at least 45 weight percent of the said calciumphosphate component is Ca (PO 6. The prosthesis material of claim 4 inwhich substantially all of said refractory component is MgAl O 7. Theprosthesis material of claim 4 in which the total mole percent of saidcalcium phosphate component consists of from 45 to 99 weight percent ofCa (PO together with from 1 to 55 weight percent of at least onecompound selected from the group consisting of CaP O Ca P O and Ca P O8. The prosthesis material of claim 4 in which the total of said calciumphosphate component provides a ratio of from 0.3 to 2.0 moles calciumper mole of phosphorous.

9. A strong dense artificial bone or tooth prosthesis material in theform of a crystalline ceramic body which has been heat-consolidated to asubstantially maximum bulk density with minimized apparent porosity,said body consisting of a mixture of discrete microcrystals of MgAl Otogether with discrete calcium phosphate microcrystals selected from thegroup consisting of whitlockite and mixtures of whitlockite with anothercalcium phosphate component selected from the group consisting of CaP OCa P O Ca P O and mixtures thereof, said mixture of whitlockite withsaid other calcium phosphate component containing at least 45 weightpercent of said whitlockite, said body containing a total of 15 topercent by weight of microcrystals of said whitlockite and said othercalcium phosphate and from 25 to percent by weight of said MgAl Omicrocrystals. I

10. The prosthesis material of claim 9 in which the total of saidwhitlockite and said other calcium phosphate component provides a ratioof from 0.3 to 2.0 moles calcium per mole of phosphorous.

11. The prosthesis material ofv claim 9 in which the total of saidwhitlockite aud said other calcium phosphate component provides a ratioof from 0.5 to 1.2 moles calcium per mole of phosphorous.

2. The prosthesis material of claim 1 in which said calcium phosphate component is whitlockite.
 3. The prosthesis material of claim 1 in which said refractory compound means is MgAl2O4.
 4. A strong dense artificial bone or tooth prosthesis material in the form of a crystalline ceramic body which has been heat-consolidated to a substantially maximum bulk density with minimized apparent porosity, said body consisting essentially of a mixture of discrete microcrystals of a calcium phosphate component selected from the group consisting of Ca3(PO4)2, CaP2O6, Ca2P2O7, Ca4P2O9, and mixtures thereof, together with discrete microcrystals of refractory component selected from MgAl2O4, AlPO4, Al2O3, and mixtures thereof, said body containing from 15 to 75 percent by weight of said calcium phosphate component and from 25 to 85 percent by weight of said refractory component.
 5. The prosthesis material of claim 4 in which at least 45 weight percent of the said calcium phosphate component is Ca3(PO4)2.
 6. The prosthesis material of claim 4 in which substantially all of said refractory component is MgAl2O4.
 7. The prosthesis material of claim 4 in which the total mole percent of said calcium phosphate component consists of from 45 to 99 weight percent of Ca3(PO4)2 together with from 1 to 55 weight percent of at least one compound selected from the group consisting of CaP2O6, Ca2P2O7, and Ca4P2O9.
 8. The prosthesis material of claim 4 in which the total of said calcium phosphate component provides a ratio of from 0.3 to 2.0 moles calcium per mole of phosphorous.
 9. A strong dense artificial bone or tooth prosthesis material in the form of a crystalline ceramic body which has been heat-consolidated to a substantially maximum bulk density with minimized apparent porosity, said body consisting of a mixture of discrete microcrystals of MgAl2O4 together with discrete calcium phosphate microcrystals selected from the group consisting of whitlockite and mixtures of whitlockite with another calcium phosphate component selected from the group consisting of CaP2O6, Ca2P2O7, Ca4P2O9, and mixtures thereof, said mixture of whitlockite with said other calcium phosphate component containing at least 45 weight percent of said whitlockite, said body containing a total of 15 to 75 percent by weight of microcrystals of said whitlockite and said other calcium phosphate and from 25 to 85 percent by weight of said MgAl2O4 microcrystals.
 10. The prosthesis material of claim 9 in which the total of said whitlockite and said other calcium phosphate component provides a ratio of from 0.3 to 2.0 moles calcium per mole of phosphorous.
 11. The prosthesis material of claim 9 in which the total of said whitlockite aud said other calcium phosphate component provides a ratio of from 0.5 to 1.2 moles calcium per mole of phosphorous. 